Phonon Bottleneck in Graphene-Based Josephson Junctions at Millikelvin Temperatures

Abstract

We examine the nature of the transitions between the normal and superconducting branches in superconductor-graphene-superconductor Josephson junctions. We attribute the hysteresis between the switching (superconducting to normal) and retrapping (normal to superconducting) transitions to electron overheating. In particular, we demonstrate that the retrapping current corresponds to the critical current at an elevated temperature, where the heating is caused by the retrapping current itself. The superconducting gap in the leads suppresses the hot electron outflow, allowing us to further study electron thermalization by phonons at low temperatures (T≲1 K). The relationship between the applied power and the electron temperature was found to be P∝T3, which we argue is consistent with cooling due to electron-phonon interactions.

Graphene-Based Josephson-Junction Single-Photon Detector

“…This implies that the GJJ should be an overdamped junction with its phase particle retrapped quickly after switching to the resistive state. However, the measured junction is hysteretic probably because the resistive state bias current self-heats the junction at low temperatures [41].…”

“…The electron heat diffusion is the heat-transfer channel out of the graphene sheet to the electrodes. However, at the superconductor-graphene contact, Andreev reflection can suppress the thermal diffusion and quench this thermal conductance channel [40,41].…”

Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions

“…I S is found to be greater, but comparable to I R throughout the gate voltage range. We have earlier attributed the origin of this hysteresis in similar resistively isolated graphene junctions to electron heating [16]. In the following, we use I S to represent the true critical current of the sample, I C .…”

Observation of vacancy-induced suppression of electronic cooling in defected graphene

“…Furthermore, it is estimated that the thermal conductance between the graphene lattice and the substrate is much higher than that due to e-p interaction. Thus, the phonon temperature T ph is approximately equal to the substrate temperature T [5,22,30].…”